如何将参数传递给工厂以创建对象？答案

【问题标题】：How to pass params into a Factory for object creation?如何将参数传递给工厂以创建对象？
【发布时间】：2015-05-12 10:40:24
【问题描述】：

我有RecipientTypesFactory，它将创建RecipientType 类型的对象。对于RecipientTypes 对象，我有以下层次结构：

public interface RecipientType{
    public abstract Object accept(RecipientTypeVisitor v);
}

public class DynamicGroupType implemetns RecipientType{

    private Integer dynamicGroupId;

    public Object accept(RecipientTypeVisitor visitor){
        return visitor.visit(this);
    }
    //GET, SET
}

public class StaticGroupType implements RecipientType{

    private Integer staticGroupId;

    public Object accept(RecipientTypeVisitor visitor){
        return visitor.visit(this);
    }
    //GET, SET
}

RecipientTypesFactory 本身如下所示：

public enum RecipientTypeEnum {
    STATIC_GROUP, DYNAMIC_GROUP
}

public class RecipientTypesFactory{
    private Map<RecipientTypeEnum, RecipientTypeCreator> creators;

    public RecipientType createRecipientType(RecipientTypeEnum t){
        return creators.get(t).create();
    }
}

我不会提供RecipientTypeCreator 的实际定义及其层次结构，因为我认为这不是很重要。

现在我有了控制器：

public class CreateMailingController{
    private RecipientTypesFactory recipientTypesFactory;
    private Integer dynamicGroupId;
    private Integer staticGroupId;
    private RecipientTypeEnum selectedType;

    //GET, SET, other staff

    public void createMailing(){
        Type t = recipientTypesFactory.createRecipientType(selectedType);
        //How to initialize t's field with an appropriate value?
    }
}

问题是RecipientTypesFactory，它的creators 对CreateMailingController 的dynamicGroupId 和staticGroupId 值一无所知。这些值是由一些用户从 Web 界面设置的。因此，工厂无法使用这些值初始化要创建的类型的相应字段。

RecipientTypesFactory 及其创建者是春豆。

问题：如何灵活地将dynamicGroupId 和staticGroupId 的值传递给工厂，避免编写switch-case 之类的代码？这可能吗？

也许为此目的还有另一种模式。事实上，工厂正在创建对象的原型。

【问题讨论】：

标签： java spring design-patterns factory

【解决方案1】：

您可以使用 map 来避免切换情况，如下所示：

private static final Map<String, RecipientType> factoryMap = Collections
            .unmodifiableMap(new HashMap<String, RecipientType>() {
                {
                    put("dynamicGroupId", new RecipientType() {
                        public RecipientType accept() {
                            return new DynamicGroupType();
                        }
                    });
                    put("staticGroupId", new RecipientType() {
                        public RecipientType accept() {
                            return new StaticGroupType();
                        }
                    });
                }
            });

    public RecipientType createRecipientType(String type) {
        RecipientType factory = factoryMap.get(type);
        if (factory == null) {

        }
        return factory.accept();
    }

【讨论】：